The Federated Service Connectivity (FSC) Core specification describes a standardised architecture for achieving inter-organisational, technical interoperability across API ecosystems. It is developed and maintained by Logius (the Dutch national government IT organisation) and VNG Realisatie.

FSC Core defines how parties, referred to as Peers, can securely discover, connect to, and manage authorisations for each other's services within a federated Group. The core principles are:

• Service discovery: Peers announce their HTTP APIs (e-services) to a shared Directory, enabling other Peers within the Group to discover available services and their providers.
• Contract management: Connections between Peers are governed by cryptographically signed, mutually agreed Contracts containing typed Grants. Contracts are negotiated in a decentralised, federated manner.
• Secure connectivity: All connections are encrypted and mutually authenticated using Mutual TLS (mTLS) and trusted digital certificates within a shared PKI trust framework. Access to services is controlled through OAuth 2.0 access tokens, ensuring only authorised systems can communicate with each other.
• Delegation: FSC Core supports delegation of service connection and publication authorisations from one Peer to another, enabling complex multi-party ecosystems.
• Automation: APIs govern all management tasks, greatly reducing administrative overhead.

The architecture defines four core components: the Manager (contract management and authorisation server), the Directory (service and peer discovery), the Inway (reverse proxy for incoming connections), and the Outway (forward proxy for outgoing connections).

The current stable release is published at https://gitdocumentatie.logius.nl/publicatie/fsc/core/.

It is released under the European Union Public Licence (EUPL).